import java.util.Scanner;

public class Main {
    public static int Sum(int n){
        if(n == 1){
            return 1;
        }else{
            return n + Sum(n-1);
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while(in.hasNextInt()){
            int n = in.nextInt();
            int result = Sum(n);
            System.out.println(result);
        }
    }
}
